The lighting information in the light probes are encoded as Spherical Harmonics basis functions. We use third order polynomials, also known as L2 Spherical Harmonics. These are stored using 27 floating point values, 9 for each color channel.
The Enlighten Global Illumination implementation in Unity uses a different spherical harmonics approach than Geomerics, the feature’s original developer, namely the notation and reconstruction method from Peter-Pike Sloan’s paper, Stupid Spherical Harmonics (SH) Tricks. Geomerics’ original approach was based on the notation and reconstruction method from Ramamoorthi/Hanrahan’s paper, An Efficient Representation for Irradiance Environment Maps.
The shader code for reconstruction is found in UnityCG.cginc and is using the method from Appendix A10 Shader/CPU code for Irradiance Environment Maps from Peter-Pikes paper.
データは内部的にこのように並べられます。
[L00: DC]
[L1-1: y] [L10: z] [L11: x]
[L2-2: xy] [L2-1: yz] [L20: zz] [L21: xz] [L22: xx - yy]
R, G, B の 9 つの係数はこのように並べられます。
L00, L1-1, L10, L11, L2-2, L2-1, L20, L21, L22, // レッドチャンネル
L00, L1-1, L10, L11, L2-2, L2-1, L20, L21, L22, // ブルーチャンネル
L00, L1-1, L10, L11, L2-2, L2-1, L20, L21, L22 // グリーンチャンネル
Unity のライトプローブシステムに関するさらに詳しい情報は、GDC 2012 の Robert Cupisz の講演 Light Probe Interpolation Using Tetrahedral Tessellations, GDC 2012 を参照してください。
2017–06–08 公開ページ
Light Probes、 5.6 で更新